1. Field of the Invention
This invention relates to float switches, and more particularly to devices of this type wherein an enclosed buoyant float member is immersed in a liquid to be gauged or monitored, and wherein movement of the member effects the opening or closing of electrical contacts disposed within the float switch housing.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
U.S. Pat. No. 3,750,124 dated July 31, 1973, issued to C. Barnes and entitled FLUID LEVEL SWITCH, illustrates a level indicator employing a float switch housing of the type adapted to be mounted in a vertical wall of a vessel such as a master cylinder, for example, and wherein a sealed magnetic-responsive reed switch is disposed in a wall of the housing. A float carrying a permanent magnet is captive in the housing, and rises or falls according to changes in the level of the liquid being monitored. As the magnet approaches the reed switch the latter is actuated, and the change is detected by a transistor amplifier stage that is arranged to illuminate an indicator lamp.
One problem with this patented construction was the necessity to accurately position the switch housing in the wall of the tank or vessel in such a way that the path of movement of the float was always along a vertical plane. This requirement constituted a distinct drawback, since the interior of the tank or vessel was often not accessible, and accordingly care had to be exercised when installing such devices.
Another float switch construction is illustrated in U.S. Pat. No. 4,467,156 dated Aug. 21, 1984, issued to D. Dvorak, and entitled LIQUID LEVEL SENSOR SWITCH. This patented device comprises a float switch housing in which there is captive a float containing an embedded contact strip. The extremities of the strip project from the float at its opposite ends. Because the strip is disposed laterally of the longitudinal axis of symmetry of the float, the latter always automatically assumes a rotary position wherein the projecting parts of the contact strip face downwardly so as to be capable of simultaneous contact on the one hand with the electrically grounded float housing and on the other hand, the inner surface of an insulated contact cup mounted in the housing. Such an arrangement does not rely upon a particular angular orientation of the switch housing for its operation. As soon as the float becomes immersed, it automatically rotates to the desired, operative position shown in FIG. 1 of the patent.
A problem with this latter patented arrangement resides in the fact that one portion of the circuit comprises the ground path provided by the wall of the vessel on which the switch is mounted. In many instances, the vessel wall does not, in fact, constitute a "good" electrical ground, that is, one which is of low impedance and relatively free of noise originating at other electrical equipment, or free of circulating ground currents. Problems with poor grounds and/or ground currents are notorious in the electronics field, and are particularly troublesome where sensitive electronic equipment is being employed. The situation is aggravated where electrical components or sub-systems are intended for use on recent model automotive vehicles of the type incorporating "on-board computers" that continuously monitor a wide variety of vehicle functions and provide the vehicle operator with information relating thereto.